This invention relates generally to the separation of particles. More specifically, the invention relates to the separation of particles suspended in a fluid through the use of acoustic forces.
Separating and sorting particles is an important activity in many applications including biological research, cellular engineering, biological and chemical analyses, and lab-on-a-chip technologies. Several methods exist for particle separation, but each has its own drawbacks. For example, magnetic, electrokinetic, and dielectrophoretic separation methods rely on the particles having an inherent charge, polarization, or magnetization. When the particles are biological cells, modifying the cells to obtain these properties can adversely impact the cell physiology and viability, rendering the techniques unusable for cellular engineering applications. Hydrodynamic separation mechanisms, including flow cytometry, can be continuous and passive, but these techniques are limited in volumetric flow rate or require contact between the particle and channel structure.
Alternatively, using acoustic forces in microfluidic particle and cell separation devices provides a promising solution to the limitations of many other methods. Acoustic particle separation is label-free and can separate particles based on physiological properties including shape, density, size, and compressibility. The use of the acoustic force is contactless and does not require any specific particle property, labeling, or tagging. Moreover, the acoustic force on biological cells does not appear to have a significant deleterious effect on the particle viability, making acoustic microfluidics an ideal method for cell separation, especially when downstream processing and analyses requires the cell physiology to remain unmodified.
According to one known acoustic method, particles are separated using standing surface acoustic waves (SAW). These types of devices, which are typically molded with soft polymers (such as in a polydimethylsiloxane), are not robust enough for use outside of a lab and are expensive to fabricate. Further, the flowrate of fluid in the device is limited because the useful standing waves are confined to a distance from the bottom surface of the channel, typically resulting in a shallow channel. It would therefore be advantageous to develop an improved device for sorting particles using acoustic forces, and a method of manufacturing the same, that are more robust and offer greater throughput.